Prevalence and distinctive biologic features of flat colorectal adenomas in a North American population

(Background & Aims) under bar: To assess the prevalence of fat and depressed (F&D) colorectal adenomas in the United States, we performed a prospective study of 211 American patients. (Methods) under bar: Dye-assisted colonoscopy was performed in the presence of both an American and a Japanese investigator, (Results) under bar: F&D lesions were found in 22.7% of patients, and these were more likely to be adenomatous than polypoid lesions (82% vs, 67%; P = 0.03) and contained mote invasive cancer (4.5% vs, 0%; P = 0.04), which also appeared to be at a disproportionately advanced stage. The average size of all F&D advanced lesions (high-grade dysplasia and cancer) was significantly smaller than comparable polypoid lesions (10.75 +/- 2.7 mm vs. 20 +/- 2.9 mm; P < 0.05), F&D adenomas showed significantly stronger fragile histidine triad (FHIT) expression and lower p53 reactivity than similarly sized polypoid adenomas, whereas proliferative and apoptotic indices were similar in both groups, <(Conclusions)under bar>: We conclude that there is a significant prevalence of colonic F&D colorectal adenomas in this country and that these lesions have significantly different biologic features than polypoid lesions. The clinical and epidemiologic implications of these findings for American patients need to be addressed in further studies.